The invention relates to a rotary table for a drill string as disclosed in the preamble of claim 1.
The rotary tables for drill strings that are common today are built having a stationary frame and a rotating part arranged therein. As a rule, a hydraulic clamp and one or two hydraulically operated slips (wedge-shaped holding collars) are mounted on the rotating part. In order to operate this hydraulic equipment, it is necessary to have hydraulic power transmission from the stationary part of the table to the rotating part.
Previously, this has been accomplished by using a hydraulic swivel which is mounted around the main shaft of the rotary table, the swivel having ports for transfer of the hydraulic medium. In practice, it has been found difficult to endow this swivel with a service life of any duration, as the seal rings used are quickly damaged by the substantial frictional heat which occurs during rotation.
It is an object of the invention to provide power transmission without the use of a swivel.
This object is achieved with the rotary table as disclosed in claim 1.
Additional features of the invention are disclosed in the dependent claims.
The invention allows the obtention of mechanical power transmission without any leakage problems. For each hydraulically operated working component. desired power transmission can be effected by means of a hydraulic motor and a hydraulic pump, but several sets of motor and pump working simultaneously on the same ring may also be used.
Each individual ring is rotatably supported in the rotating part, preferably by means of simple slide bearings. The gearwheels on the input shaft of the hydraulic pumps are in permanent driving engagement with the internal toothing of the respective ring whilst the driving interaction between the gearwheels on the output shafts of the hydraulic motors and the respective external toothing is capable of engagement and disengagement. Two-way couplings may be used for this engagement and disengagement, but a preferred embodiment is one in which the gearwheel is brought into and out of driving engagement with the external toothing, and an especially preferred embodiment is one in which the actual hydraulic motor is moved thereby bringing the associated gearwheel into and out of engagement with the external toothing. This motion may advantageously take place with the aid of a hydraulic working cylinder.
The hydraulic motors and working cylinders may be controlled from a control cabin and can be operated individually and in both directions, thereby enabling the hydraulic pumps which are connected to their respective units, either a clamp or slips, to operate these units in both directions.
A rotary table usually has several hydraulic main motors for the operation of the rotating part. It is therefore advantageous to provide the hydraulic system with an interlock in the control system to prevent the hydraulic main motors from being operated whilst the motors for clamps and slips are in operation.